We have moved into a home with an inground marcite finish pool. It is 11000 gallons. We know very little about it and have never owned a pool before, but when we decided on this house we found TTFP and have been reading up.
About a week after moving in, about a dozen dark brown spots, varying in size from dime to nickel sized, began appearing around the drain at the deep end of the pool. Reading here, the suggestion was to lower the pH to 6.8 with muriatic acid and scrub the bejeezus out of them, and then raise the pH when we get the stains out. We've been doing this the past 2-3 days without much improvement. The calcium hardness is quite high, and when I run that particular test, I am getting purple before I get blue, which makes me think there is metal in the water.
The water itself is relatively clean and clear. I do feel like the marcite surface is dingy, and don't really know how to remedy that. Also, the drain cover has been stained since we moved in.
Today's tests with our Taylor K-2006 kit:
These are all in line with the pool manufacturer's recommendations, except for the CH, and the TA is maybe a touch low, but had been fine until today at 80-100.
These photos were taken at night, so they don't necessarily accurately depict the color of the water.